1. Field of the Invention
The invention relates to a controller for a continuously variable transmission, which executes automatic vehicle speed control for controlling an actual vehicle speed based on a set target vehicle speed irrespective of a required power amount based on driver's operation.
2. Description of Related Art
There is well known a controller for a continuously variable transmission, which calculates the speed ratio control required power amount based on a target driving force for automatically controlling an actual vehicle speed and then calculates a target speed ratio of the continuously variable transmission based on the speed ratio control required power amount. This is, for example, the shift controller for a continuously variable transmission, described in Japanese Patent Application Publication No. 2011-202565 (JP 2011-202565 A). JP 2011-202565 A describes that shift control is executed by calculating an accelerator operation amount for cruise control based on a horsepower required to reach a target vehicle speed that is set at the time of cruise control and then setting a target speed ratio of the continuously variable transmission based on the accelerator operation amount for cruise control and an actual vehicle speed. JP 2011-202565 A further describes that a rapid change in the accelerator operation amount for cruise control after a downshift resulting from acceleration is prevented by setting the characteristic curve of the accelerator operation amount for cruise control along an equal horsepower line in a map that specifies the accelerator operation amount for cruise control and, as a result, shift hunting is suppressed.
Incidentally, suppressing a change in the accelerator operation amount for cruise control is useful in stabilizing a speed ratio by suppressing a change in the speed ratio, while, on the other hand, the response of a shift to a required horsepower is decreased. In the meantime, when the characteristic between an accelerator operation amount and an engine torque is adapted to a vehicle, it is conceivable to provide an engine operating range in which the degree of a change in accelerator operation amount to a change in engine torque is large and an engine operating range in which the degree is small. In this case, if a change in accelerator operation amount for cruise control is suppressed during execution of automatic vehicle speed control irrespective of such a difference in engine operating range, there is a concern that a driver experiences a feeling of strangeness (for example, a feeling of insufficient acceleration, or the like). The above-described inconvenience is not publicly known.